The rise of fully turbulent flow

TL;DR

This paper uncovers the bifurcation scenario and front dynamics that organize the transition from laminar to fully turbulent pipe flow, bridging the understanding gap between onset and fully developed turbulence.

Contribution

It introduces a new interpretation of flow as a bistable system with nonlinear propagation, explaining the transition and front dynamics in turbulence.

Findings

Identification of the bifurcation scenario leading to turbulence

Explanation of front dynamics in transitional flows

Flow interpreted as a bistable system with nonlinear propagation

Abstract

Over a century of research into the origin of turbulence in wallbounded shear flows has resulted in a puzzling picture in which turbulence appears in a variety of different states competing with laminar background flow. At slightly higher speeds the situation changes distinctly and the entire flow is turbulent. Neither the origin of the different states encountered during transition, nor their front dynamics, let alone the transformation to full turbulence could be explained to date. Combining experiments, theory and computer simulations here we uncover the bifurcation scenario organising the route to fully turbulent pipe flow and explain the front dynamics of the different states encountered in the process. Key to resolving this problem is the interpretation of the flow as a bistable system with nonlinear propagation (advection) of turbulent fronts. These findings bridge the gap between our understanding of the onset of turbulence and fully turbulent flows.